Multiple transducer magnetic head

ABSTRACT

A magnetic reproducing head having a plurality of electromagnetic transducers spaced within the magnetic influence of one another. Magnetic shields are interposed in the space between each transducer to eliminate the cross-coupling of magnetic lines of flux between adjacent transducers within the body of the magnetic head. An eddy current generating member is mounted to eliminate the cross-coupling of magnetic lines of flux externally to the face of the magnetic head.

United States Patent [1 1 Kruklitis MULTIPLE TRANSDUCER MAGNETIC HEAD [75] Inventor: Karlis Kruklitis, Plymouth, Mich.

[731 Assignee: Burroughs Corporation, Detroit,

Mich.

[22] Filed: Oct. 22, 1971 I21] Appl. No.: 191,897

Related US. Application Data [63] Continuation of Ser. No. 833,909, June 17, 1969,

abandoned.

[52] US. Cl. 179/1002 C, 340/l74.1 F [51] Int. Cl. ..Gl1b 5/16, G1 1b 5/28 [58] Field of Search 179/100.2 C;

r 340/1741 F; 346/74 MC [56] References Cited UNITED STATES PATENTS 2,596,912 5/1952 Nygaard 179/1002 C Sept. 11, 1973 2,263,485 11/1941 Clopton 179/1002 C 2,361,752 10/1944 Eilenberger 3,065,311 11/1962 Komei 179/1002 C 3,432,839 3/1969 Stapper 179/1002 C Primary Examiner-James W.-Moffitt Attorney-Paul W. Fish et a1.

57 ABSTRACT A magnetic reproducing head having a plurality of electro-magnetic transducers spaced within the magnetic influence of one another. Magnetic shields are in terposed in the space between each transducer to eliminate the cross-coupling of magnetic lines of flux between adjacent transducers within the body of the magnetic head. An eddy current generating member is mounted to eliminate the cross-coupling of magnetic lines of flux externally to the face of the magnetic head.

3 Claims, 8 Drawing Figures PATENTED SEPI 1 I973 KARL/S KRUKL/T/S.

ATTORNEY.

INVEN 'I OR.

MULTIPLE TRANSDUCER MAGNETIC HEAD This is a continuation of application Ser. No. 833,909, filed June 17, I969, and now abandoned.

PRIOR ART Prior art multiple transducer magnetic heads have required spacing of the electro-magnetic transducers to avoid the cross-coupling of magnetic lines of flux between adjacent transducers. This spacing provides a large reluctance path to the cross-coupling magnetic circuit thereby minimizing the signal from adjacent passive transducers due to magnetic flux coupling from the active transducer. To reduce the spacing between transducers, several types of shields have been used externally to the multiple transducer magnetic head to shield each individual electro-magnetic transducer from cross-coupling lines of magnetic flux external to the head. These external shields increase the relucing or read head comprising in general a casing 12 I opened at one end, a body 14 within the casing and a tance in the magnetic circuit between the transducer SUMMARY OF INVENTION A multiple transducer magnetic head having a plurality of closely spaced parallel electro-magnetic transducers and having a magnetic shield between adjacent electro-magnetic transducers. The front gap of each electro-magnetic transducer is aligned along'a single plane extending orthogonal to the broadside of the transducers. An eddy current generating member overlies the several transducers to eliminate the external cross-coupling lines of magnetic flux between adjacent transducers.

DESCRIPTION or THE DRAWINGS In the drawings:

FIG. 1 is a plan view of a netic head;

FIG. 2 is a front elevation of the head of FIG. 1;

FIG. 3 is an enlarged front elevation view of the ga area of the head of, FIG. 1; I j

FIG. 4 is a fragmentary sectional view taken along line 4-4 of FIG. 3; I I

FIG. 5 is a fragmentary sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is a fragmentary sectional perspective view of the magnetic head with certain parts omitted for clar- "y multiple transducer mag- IG. 7 is a diagrammatic view illustrating the objectional flux lines of the prior art;

FIG. 8 is a fragmentary sectional view taken along lines 88 of FIG.6 illustrating the improvement of the present magnetic head. I I

DETAILED DESCRIPTION Referring to the drawings there is shown a reproducplurality or stack of electro-magnetic transducers 16 mounted on the body and positioned at the open end of the casing. The casing 12 is fabricated from a metallic material and the body is fabricated from a non metallic, non-magnetic material such as an epoxy. The body 14 functions to support and retain the plurality of electro-magnetic transducers 16 in the casing.

At the open end of the casing 12, the reproducing head 10 is basically truncated or V"-shaped having a narrow flat surface 18 at the apex of the V.

Each of the electro-magnetic transducers 16, in the preferred embodiment there are thirty, comprises a flat laminated loop or ring-shaped core 20 having a single front gap 22 and parallel broadsides 24, and a flat copper winding 26 wound around one end of the core. The front gap 22 of each transducer core 20 is defined by the ends 27 of each core 20 being positioned in opposed spaced apart relationship to each other. In the drawings, the laminations are not shown for reasons of clarity. Each transducer 16 is supported by a coresupporting member. 28 having an aperture therein substantially the same size and shape as in the transducer core-The core supporting member 28 is'substantially the same width as the transducer core 20. Positioned on either side of the transducer core 20 and in contact'with both the broadside of the core and the core supporting member 28 are a pair of insulating members 30 of a nonmagnetic material such as half hard brass. Adjacent to and in contact with each of the. insulating members 30 is a high permeability magnetic shield; 32 foil which functions to prevent transformer coupling between adjacent windings 26 thereby serving to eliminate unwanted signals commonly called cross-talk.

In the preferred embodiment the thirty electromagnetic transducers 16 are positioned with their core broadsides 24 parallel to each other within a space of slightly greater than A inch. As previously mentioned, interposed in the space between each transducer are two insulating members 30 with a magnetic shield 32 therebetween. In orderto accomplish this packaging density of transducers wherein each transducer is within the magnetic influence or effective flux coupling of the adjacent transducer, .the windings 26 are alternately aligned in two spaced-apart rows. The distance between each transducer 16 is substantially less than the width of a transducer core 20. I

The front gap 22 of each transducer is aligned along a plane orthogonal to the broadsides24 of the cores 20 and centrally positioned along the flat surface 18 of the reproducing head at the open end of the casing. Within the .gap length, which is one thousandth of an inch,

thereispositioned a magnetic shim 34 between a pair I of shim insulating members 36. The shim insulating I members 36 are in contact with the loop ends 27 of the passing document 40. Asillustrated, the lines of magnetic flux emitting from the character 38, magnetically couple the character to the adjacent transducers with one of the innermost lines 42 of magnetic flux crossing the front gap 22 thereby not generating a current in the winding 26. One of the outermost lines 44 of magnetic flux is shown as passing through the transducer core 20 and magnetically coupling with the winding 26 to generate an electric signal therefrom.

In prior art multiple transducer magnetic heads, the center to center distance between adjacent electromagnetic transducers must be large enough to prevent the cross-coupling lines 46 of magnetic flux from one transducer to an adjacent transducer from inducing an electrical signal in the adjacent transducer. Also, the lines 48 of magnetic flux emitting from an encoded magnetic character 38 which do not magnetically couple with the nearest transducer, must not substantially effect the adjacent transducers. As shown, the magnetic lines of flux from an encoded magnetic character not only couple with the nearest transducer but with each adjacent transducer. Also, the cross-coupling lines 46 of magnetic flux emitting from the middle transducer magnetically couple with each adjacent transducer. As is well known, the magnetic shield 32 in the space between adjacent transducers 16 functions to eliminate the cross-coupling of magnetic flux within the body 14 of the reproducing head but does not shield adjacent transducers from the external cross-coupling lines 46 of magnetic flux.

To achieve closer spacing of the electro-magnetic transducers l6 and to substantially eliminate external cross-coupling lines 46 of magnetic flux as previously mentioned, the outer surfaces of the reproducing head 10 adjacent to thefront gap 22 area have each been covered by a layer of electrically conductive material serving as an eddy current generating member 50. This member 50, which in the preferred embodiment is a copper plate, overlies and is in an abutting relationship with edge portions of each of the transducer cores 20 facing outwardly of the body 14. The eddy current generating member 50, in the preferred embodiment, does not extend across the flat portion 18 of the reproducing head 10 so as to not introduce additional reluctance in the magnetic circuit between encoded magnetic character 38 and the electro-magnetic transducers 16.

Equating the diagrammatic representations of FIGS. 7 and 8 with the perspective of FIG. 6, the diagrammatic view of FIG. 8 represents a sectional view taken through the eddy current generating member 50.

The eddy current generating member 50 is a very low resistivity, less than 2.5 microhms-centimeter, nonmagnetic metallic material. Copper, which has a resistivity of 1.682 microhm-centimer was selected in the preferred embodiment over gold or silver for reasons of economy. All three metals are classified as diamagnetic materials wherein an applied magnetic field such as from the cross-coupling lines 46 of magnetic flux, is slightly reduced due to the alternation of the atomic electron orbits produced by the field. When diamagnetic materials are placed in a magnetic field, they tend to orientate themselves in the direction of the field, with their magnetism opposing that of the field. Therefore, the cross-coupling lines 46 of flux generate an eddy current within the eddy current generating member 50 which in turn generates a magnetic field in opposition to the field of the cross-coupling lines of magnetic flux.

The eddy current generating member .50 overlies the edge portions of the electro-magnetic transducer cores 20 and may extend to the casing 12 where it is secured by any bonding means such as electrolytic plating.

The eddy current generating member 50 also functions'to prevent external electro-magnetic signals from adversely effecting the electro-magnetic transducers 16 within the reproducing head 10. Adverse effects are the generation of electrical signals from the transducer winding 26 from spurious signals external to the reproducing head 10. These spurious signals are frequently the cause of electrical noise on the electro-magnetic transducer signal lines.

There has been shown and described a multiple transducer reproducing head'l0 having an eddy current generating member 50 overlying theexposed ends of the electro-magnetic transducerv cores 20. The eddy current generating member 50 eliminates the crosscoupling lines 46 of magnetic flux between adjacent transducers 16 and thereby achieves a closer spacing between the center lines of the electro-magnetic transducers 16.

What is claimed is:

1. In a low frequency multiplechannel magnetic transducing head for reading magnetic. inked characters comprising a stack of similar closely spaced apart thin flat magnetic transducing core elements each forming a closed magnetic circuit except for the provision of a front gap and so mounted by non-magnetic material to exhibit a general truncated formation in-.

cluding a pair of sloping walls coverging toward one another but terminating short of convergence to form a narrow flat surface therebetween and to locate the gaps in the core elements in the .fiat surface in alignment with one another for sensing magnetic: inked characters on a record medium relatively movable closelypast the head, the improvement comprising:

magnetic means disposed along said aligned gapstodecrease the reluctance of said gaps, non-magnetic means insulating said magnetic means from said sloping walls, and, p, athin layer of electrically conductive material contactually overlying each of said pair of sloping walls formed by the stack of magnetic core elements and covering substantially the surface area of each .of the sloping walls, said electrically conductive layers terminating flush with the plane of the flat surface leaving exposed the aligned frontigaps of the magnetic core elements, said electrically. conductive layers responding to cross-coupling lines of magnetic flux between adjacent magnetic core .elemerits of the stack and passing through the conduc-.

tive layer for generating eddy currentsin the layers which .in turn generate magnetic flux lines operat ing in opposition to said cross-couplingflines of magnetic flux thereby substantially reducing inter channel crosstalk.

2. In a low frequency multiplechannel. magnetic transducing head according to claim 1 wherein'said electrically conductive layers approach the plane of the flat surface in a taper of decreasing material thickness so that the extremity of the taper terminates at the plane of the surface.

3. In a low frequency multiplechannel. magnetic transducing head according to claim 1 whereinsaidv electrically conductive layers arecomposed ofdiamagnetic material having a resisitivity less than 2.5-

microhms-centimeter.

i l l i ll 

1. In a low frequency multiple channel magnetic transducing head for reading magnetic inked characteRs comprising a stack of similar closely spaced apart thin flat magnetic transducing core elements each forming a closed magnetic circuit except for the provision of a front gap and so mounted by non-magnetic material to exhibit a general truncated formation including a pair of sloping walls coverging toward one another but terminating short of convergence to form a narrow flat surface therebetween and to locate the gaps in the core elements in the flat surface in alignment with one another for sensing magnetic inked characters on a record medium relatively movable closely past the head, the improvement comprising: magnetic means disposed along said aligned gaps to decrease the reluctance of said gaps, non-magnetic means insulating said magnetic means from said sloping walls, and a thin layer of electrically conductive material contactually overlying each of said pair of sloping walls formed by the stack of magnetic core elements and covering substantially the surface area of each of the sloping walls, said electrically conductive layers terminating flush with the plane of the flat surface leaving exposed the aligned front gaps of the magnetic core elements, said electrically conductive layers responding to cross-coupling lines of magnetic flux between adjacent magnetic core elements of the stack and passing through the conductive layer for generating eddy currents in the layers which in turn generate magnetic flux lines operating in opposition to said cross-coupling lines of magnetic flux thereby substantially reducing interchannel crosstalk.
 2. In a low frequency multiple channel magnetic transducing head according to claim 1 wherein said electrically conductive layers approach the plane of the flat surface in a taper of decreasing material thickness so that the extremity of the taper terminates at the plane of the surface.
 3. In a low frequency multiple channel magnetic transducing head according to claim 1 wherein said electrically conductive layers are composed of diamagnetic material having a resisitivity less than 2.5 microhms-centimeter. 